Methods and Apparatus for Overload Control of Prioritized Message Flows in a State Machine Execution Environment

ABSTRACT

Methods and apparatus are provided for overload control of prioritized message flows in a state machine execution environment. A state machine employs a flow graph associated with a system. The flow graph provides a flow control mechanism that defines a plurality of states and one or more transitions between the states. Tokens circulate within the flow graph and execute functions during the transitions between the states. The state machine parses one of the tokens to extract one or more predefined information elements; assigns a priority to the token based on the extracted information elements and a state occupancy of the token, wherein the assigned priority controls an order in which the token is processed; assesses an overload status of the system and selectively discards one or more of the tokens based on the assigned priority and assessed overload status. One or more tokens can be selectively discarded based on the assessed overload status and a closeness measure indicating how close a given token is to placing the system in a quiescent state.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to U.S. patent application Ser. No. 12/040,239, filed Feb. 29, 2008, entitled “Method and Apparatus for Prioritizing Message Flows in a State Machine Execution Environment,” incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to message processing techniques and, more particularly, to techniques for managing overload control of prioritized message flows in a state machine execution environment.

BACKGROUND OF THE INVENTION

Software applications are often constructed using an abstract state description language. Voice over Internet Protocol (IP) (or VoIP) call control applications, for example, have been realized by using a high level description language to describe the data processing and message exchange behavior of a VoIP Media Gateway Controller (MGC). In this system, an “execution engine” accepts a high level “graph language” used by the execution engine to create internal data structures that realize the VoIP MGC behaviors described in the input graph language. The combination of the execution engine and the input file that contains the graph language describing the VoIP MGC behavior results in a system that exhibits the desired MGC processing characteristics.

The description language supports an enhanced transition graph model. As a result, the computation can be best understood as a graph consisting of a set of nodes connected by arcs. Using this model, there may be many tokens that exist at a given node. The arcs represent transitions that tokens take between nodes. Tokens traverse arcs in response to events that can be derived from either timers or messages.

In many systems, especially those that implement VoIP call control, the system must perform predictably in the face of high demand, such as spikes of traffic. Typically, a call flow will be started with an event in the form of a message, generated on behalf of a user, when a user goes off-hook or completes entering a telephone number of a desired destination. The initial event will be followed by a series of message exchanges used by the specific protocol to move the call into a quiescent state.

In a conventional system under heavy or overload conditions, all messages (and therefore transitions between states) will be given an equal priority. This may result in a delay for the completion of a call setup message sequence (representing a call accepted by the system and already in progress), as requests for new service (e g, a new call) will compete for resources with calls that are already in the process of being torn down. Thus, additional resources will be expended for a given offered load, as the system will not give precedence to a call in a tear-down phase that would be returning resources to the system.

A need therefore exists for an improved state machine execution environment that prioritizes message flows. Yet another need exists for a state machine execution environment that provides overload control with message prioritization.

SUMMARY OF THE INVENTION

Generally, a method and apparatus are provided for overload control of prioritized message flows in a state machine execution environment. According to one aspect of the invention, a state machine is disclosed that employs a flow graph that is associated with a system and provides a flow control mechanism. The flow control mechanism defines a plurality of states and one or more transitions between the plurality of states, wherein one or more tokens circulate within the flow graph and execute functions during the one or more transitions between the states. The disclosed state machine parses one of the tokens to extract one or more predefined information elements; assigns a priority to the token based on the extracted information elements and a state occupancy of the token, wherein the assigned priority controls an order in which the token is processed; assesses an overload status of the system and selectively discards one or more of the tokens based on the assigned priority and assessed overload status.

For example, the extracted information elements can comprise one or more name/value pairs. As used herein, the state occupancy is a position of the token in the flow graph. The assigned priority can be based, for example, on an effect that a particular transition by the token will have on other resources. In further variations, the assigned priority can be based, for example, on one or more of an amount of computation resources required by the token; a time sensitivity of the token; a determination of whether the token includes idle time and a determination of whether a response is expected by another entity to the token. In one embodiment, the flow graph is a call flow graph that controls a processing of call control messages and wherein the functions include one or more of sending messages to other tokens and to external devices; and parsing incoming messages from other tokens or external devices.

According to another aspect of the invention, a higher priority can be assigned to a token that will trigger a transition that will return one or more currently used system resources to an available status or a quiescent state. In this manner, one or more tokens can be selectively discarded based on the assessed overload status and a closeness measure indicating how close a given token is to placing the system in a quiescent state. The state machine can optionally assign the token to one of a plurality of priority-based queues. In addition, the state machine can optionally dynamically adjust a priority assigned to the token based on an overload status. The state machine can discard one or more lower priority tokens when a priority queue of a predefined priority level is full.

A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary network environment in which the present invention can operate;

FIG. 2 illustrates an implementation of the portable call agent of FIG. 1 using a state machine execution environment incorporating features of the present invention;

FIG. 3 illustrates an exemplary call flow graph;

FIG. 4 illustrates an exemplary portion of a call flow graph incorporating features of the present invention;

FIG. 5 illustrates the processing of VoIP control messages in accordance with an embodiment of the present invention;

FIG. 6 illustrates exemplary pseudo-code for a message handling process with overload control that incorporates features of the present invention; and

FIG. 7 illustrates an exemplary spectrum 700 that allows one of a plurality of overload policies to be assigned to a given command based on the proximity of the command to a quiescent state.

DETAILED DESCRIPTION

The present invention provides methods and apparatus for managing overload control of prioritized messages flows within a formal state machine execution environment. As used herein, a flow control mechanism defines a plurality of states (or nodes) in a graph and the transition arcs between such states. The disclosed state machine execution environment employs an explicit flow control mechanism and a two-stage processing of messages. In a first stage, a preliminary pass is performed over messages (or selected portions thereof) to extract information, such as one or more name/value pairs, that can be employed to prioritize the message. In a second stage, the messages are processed using the context of the computation to choose a specific message parsing behavior.

Using a combination of the preliminary parsing in the first stage and the position of the target token in the call flow graph (referred to herein as the “state occupancy” of the token), a priority is assigned to the subsequent processing of the message within the formal state machine execution environment. The assigned priority can be used to control the order in which messages are processed.

In general, the prioritization can be based on, for example, the effect that a particular state transition has on other resources. In various embodiments, the prioritization can be based, for example, one or more of the amount of required computation resources, the time sensitivity of the message, whether the required message processing includes idle time, and whether a prompt response is expected to the message. If no response is expected, the recipient can typically replay the message out of order. In addition, using the assigned priority, call flows that are in the process of being set up, or being torn down, can be assigned a higher priority, thus minimizing the peak resources needed by the system to function responsively and those providing extra margin for handling overload.

According to another aspect of the invention, a conditional prioritization technique can be employed. Building upon the information that is available to the execution engine as a side effect of prioritization of the messages, the queue length of the lower priority messages can be used to set a dynamic policy for treatment of message processing. For example, the disclosed overload control method can use the queue length of lower priority messages to set a dynamic policy for treatment of message processing. Since messages are partially processed upon reception, the disclosed mechanism can be used to selectively discard unassociated messages (i.e., messages that are not part of an existing call flow/computation) and/or unsolicited messages (i.e., messages that are not expected responses).

In a conditional prioritization implementation, as the load on the system reaches a predefined threshold, such as a “yellow zone” queue length of the lower priority messages currently waiting processing, the system would start to discard messages currently unassociated with a current flow. If the queue length of the lower priority messages continues to grow, reaching a predefined “red zone,” the system begins to discard messages that are associated but are unsolicited. As the queue length shrinks below each of the thresholds described above, the system ceases discarding the related class of messages. In this way, the system will maximize its ability to properly handle extreme spikes in message traffic, minimizing the impact on memory and processing burden on the host system.

While the present invention is illustrated herein in the context of an exemplary Voice over Internet Protocol Media Gateway Controller, the present invention may be employed in any environment where a number of tokens circulate within a flow graph in a state machine and execute functions during transitions between states, as would be apparent to a person of ordinary skill in the art.

FIG. 1 illustrates an exemplary network environment 100 in which the present invention can operate. The exemplary network environment 100 is a Voice over Internet Protocol call control environment. As shown in FIG. 1, a portable call agent 110 connected to one or more VoIP Gateways 130-1 through 130-N by an IP network 120, route Voice over Internet Protocol telephone calls to or from one or more end users 140-1 through 140-N. Generally, the portable call agent 110 provides multi-protocol VoIP call control, in a known manner. For example, the portable call agent 110 can provide protocol translation between one or more of the following well-known VoIP protocols: SIP, H 248, MGCP, IPDC/Q 931 and SS7/M2UA.

As discussed further below in conjunction with FIG. 3, the portable call agent 110 reduces the call flow into a combination of state and name/value pairs to enable the above-mentioned protocol inter-working. It is noted that in a distributed model, multiple instances of the portable call agent 110 can create dynamic associations to provide call control to end users.

As discussed hereinafter, in the exemplary embodiment, the functionality of the present invention resides in the portable call agent 110. In this example, the VoIP control is being managed by the portable call agent 110, and the desired behavior is created by managing the messages at the portable call agent 110 without burdening the gateway 130 with additional processing requirements.

FIG. 2 illustrates an implementation of the portable call agent 110 using a state machine execution environment incorporating features of the present invention. As previously indicated, software applications, such as the exemplary Voice over Internet Protocol (IP) (or VoIP) call control applications, are often constructed using an abstract state description language. As shown in FIG. 2, the portable call agent 110 includes an execution engine 220 (i.e., a virtual machine) that accepts a graph language 210 that describes the media gateway controller functions. The graph language 210 is used by the execution engine 220 to create internal data structures 230 that realize the VoIP MGC behaviors described in the input graph language 210. The combination of the execution engine 220 and the input file 210 that contains the graph language describing the VoIP MGC behavior results in a system that exhibits the desired MGC processing characteristics. Thus, the portable call agent 110 is a combination of a protocol engine 220 and a set of data files 230.

As discussed further below in conjunction with FIG. 3, the data files 230 explicitly define the call flow in terms of state transitions and message translations. Generally, as discussed further below, a call flow is read into the portable call agent 110 and instantiated at start up time.

FIG. 3 illustrates an exemplary call flow graph 300 (or more generally, a “flow graph”). The desired service is realized in the portable call agent 110 using a flow representation of the computation. As shown in FIG. 3, the call flow graph 300 provides a flow control mechanism that defines a plurality of states (or nodes) 310-1 through 310-N (hereinafter, collectively referred to as states 310) and the transition arcs 320-1 through 320-N (hereinafter, collectively referred to as transitions 320) between such states 310.

Generally, a number of tokens (corresponding to messages or sessions in the exemplary VoIP environment) circulate within the graph 300 and execute functions during transitions 320 between states 310. For example, when an unassociated message is received and is validated, a new session may be created by way of creating a new token. Subsequent messages may be associated with a particular session and therefore no new tokens are created for those messages. In the exemplary VoIP environment, the transition functions include sending messages to other tokens and to external devices; and parsing incoming messages from other tokens or external devices.

FIG. 4 illustrates an exemplary portion of a call flow graph 400 incorporating features of the present invention. Generally, a “graph function” is a function invoked at an entry state that causes the engine to pass control back to the calling state rather than to an arbitrary next state. The graph function comprises one or mote states. The effect is that there is a set of states that are partitionable, starting with the entry state and including all of the reachable states up to the state that uses a “graph return” to send control back to the entry state. A portion of a graph, such as the graph 300 of FIG. 3, can be considered to be a set of graph functions.

As shown in FIG. 4, an entry state 410 has a first transition 415 to an intermediate state 420. The intermediate state 420 has a second transition 425 to a returning state 430. The returning state 430 has a third transition 435 that uses a graph return to pull the next state from a graph stack 450, in a known manner. The “graph call” function executed at the entry state 410 pushes its own state number onto the graph stack 450 to be used later by the “graph return” method invoked by the returning state 430

FIG. 5 illustrates the processing of VoIP control messages 515 in accordance with an embodiment of the present invention. As shown in FIG. 5, the VoIP control messages 515, such as an exemplary input message parsing file 520, are applied to the exemplary call flow graph 300 of FIG. 3. The call flow graph 300 is defined by a call flow definition file 550. Thus, the call flow definition file 550 is an example of the input graph language 210 of FIG. 2

As previously indicated, a number of tokens (e.g., corresponding to messages 520) circulate within the graph 300 and execute functions during transitions between states. For example, when an unassociated message is received and is validated, a new session may be created by way of creating a new token. Subsequent messages may be associated with a particular session and therefore no new tokens are created for those messages. In the exemplary VoIP environment, the transition functions include sending messages to other tokens and to external devices; and parsing incoming messages from other tokens or external devices. In the example shown in FIG. 5, a transition function triggers the generation of an output message generation file 530.

FIG. 6 illustrates exemplary pseudo-code for a message handling process 600 incorporating features of the present invention. As shown in FIG. 6, the message handling process 600 initially determines during step 605 if any priority queue is full. If any priority queue is full, then the oldest message is selected during step 610 from the highest priority queue. The selected message is processed and control is passed to the associated token before the process 600 returns.

During step 620, the process determines if there are additional incoming messages to be processed that are waiting on the server input by the state machine. If there are additional incoming messages, the message is partially parsed during step 625 to recover information that relates the message to a particular token. If a token not found, then the message is assigned to a base token.

A test is performed during step 630 to determine if the state machine is in an overload condition. If the state machine is in an overload condition, the state of the token is examined during step 635 to determine an appropriate input message handling priority. The message is then placed in a priority queue.

If it is determined during step 640 that the message has an immediate priority, then the message is processed to completion and control is passed to that token. Thereafter, the process 600 breaks out of the while “incoming messages” loop during step.

If the message does not have an immediate priority, then the process 600 continues at the top of the while “incoming messages” loop during step 650 to check for more messages waiting on input.

If the state machine is not in an overload condition, the message is processed during step 660 and control is passed to the token. Thereafter, the process 600 breaks out of the while “incoming messages” loop during step 665.

If it is determined during step 675 that either priority queue is full, then the oldest message is selected during step 680 from highest priority queue, the selected message is processed, and control is passed to the associated token. Thereafter, the process 600 breaks out of the while “incoming messages” loop during step 685

During step 698, the process 600 selects the oldest message from the highest priority queue, processes the selected message and passes control to the associated token before returning.

In a further variation of the present invention, there could be a number of predefined levels of overload, that can each lead to one or more predefined actions being taken. Under an extreme overload condition, for example, if the received message is not above a predefined priority level, then rather than placing the message in a queue, the message can simply be discarded. The level of priority can dynamically change depending on the overload status of the state machine. When a priority queue of a predefined priority level is full, messages of a lower priority level are discarded. In addition, the priority of a message may be a function of the state of the current token and the priority tag on the message or packet itself.

In this manner, aspects of the present invention allow one or more tokens to be selectively discarded based on an assigned priority and an overload status. In one implementation, tokens ate selectively discarded based on a predefined overload policy and the assigned priority. For example, a policy can give precedence to a call in a tear-down phase that would be returning resources to the system. For example, a policy may discard new commands (or transactions) over responses to commands that have already been accepted. In this manner, the resolution of pending transactions is given precedence over the processing of new commands that generally have a greater overall demand for resources.

Thus, a semantic analysis is applied to messages to evaluate the impact of accepting the messages on the available resources based on the type of function. For example, commands can be processed to evaluate a closeness measure indicating how close a given command is to placing the system in a quiescent state. As indicated above, a policy may discard new commands (typically, a new transaction) over responses to commands that have already been accepted (generally closer to a quiescent state). Likewise, in a SIP environment, an INVITE command will typically be associated with a new transaction, and a BYE command and an acknowledgement message will typically be closer to a quiescent state and will result in resources being released FIG. 7 illustrates an exemplary spectrum 700 that allows one of a plurality of overload policies to be assigned to a given command based on the proximity of the command to a quiescent state.

In a further variation, an overload policy can be specifically established for one or more commands requiring special treatment. A heartbeat message, for example, may require that the number of consecutive messages that are discarded does not exceed a predefined threshold, in order to avoid a system reset. Thus, an appropriate overload policy can be established.

While FIG. 6 shows an exemplary sequence of steps, it is also an embodiment of the present invention that the sequence may be varied. Various permutations of the algorithm are contemplated as alternate embodiments of the invention.

In addition, while exemplary embodiments of the present invention have been described with respect to processing steps in a software program, as would be apparent to one skilled in the art, various functions may be implemented in the digital domain as processing steps in a software program, in hardware by circuit elements or state machines, or in combination of both software and hardware. Such software may be employed in, for example, a digital signal processor, micro-controller, or general-purpose computer. Such hardware and software may be embodied within circuits implemented within an integrated circuit.

Thus, the functions of the present invention can be embodied in the form of methods and apparatuses for practicing those methods. One or more aspects of the present invention can be embodied in the form of program code, for example, whether stored in a storage medium, loaded into and/or executed by a machine, or transmitted over some transmission medium, wherein, when the program code is loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention. When implemented on a general-purpose processor, the program code segments combine with the processor to provide a device that operates analogously to specific logic circuits. The invention can also be implemented in one or more of an integrated circuit, a digital signal processor, a microprocessor, and a micro-controller.

System and Article of Manufacture Details

As is known in the art, the methods and apparatus discussed herein may be distributed as an article of manufacture that itself comprises a computer readable medium having computer readable code means embodied thereon. The computer readable program code means is operable, in conjunction with a computer system, to carry out all or some of the steps to perform the methods or create the apparatuses discussed herein. The computer readable medium may be a recordable medium (e.g., floppy disks, hard drives, compact disks, memory cards, semiconductor devices, chips, application specific integrated circuits (ASICs)) or may be a transmission medium (e.g., a network comprising fiber-optics, the world-wide web, cables, or a wireless channel using time-division multiple access, code-division multiple access, or other radio-frequency channel). Any medium known or developed that can store information suitable for use with a computer system may be used. The computer-readable code means is any mechanism for allowing a computer to read instructions and data, such as magnetic variations on a magnetic media or height variations on the surface of a compact disk.

The computer systems and servers described herein each contain a memory that will configure associated processors to implement the methods, steps, and functions disclosed herein. The memories could be distributed or local and the processors could be distributed or singular. The memories could be implemented as an electrical, magnetic or optical memory, or any combination of these or other types of storage devices. Moreover, the term “memory” should be construed broadly enough to encompass any information able to be read from or written to an address in the addressable space accessed by an associated processor. With this definition, information on a network is still within a memory because the associated processor can retrieve the information from the network.

It is to be understood that the embodiments and variations shown and described herein are merely illustrative of the principles of this invention and that various modifications may be implemented by those skilled in the art without departing from the scope and spirit of the invention. 

1. A state machine, comprising: a memory containing a flow graph associated with a system that provides a flow control mechanism, wherein said flow control mechanism defines a plurality of states and one or mote transitions between said plurality of states, wherein one or more tokens circulate within said flow graph and execute functions during said one or mole transitions between said states; and at least one processor, coupled to the memory, said at least one processor operative to: parse one of said tokens to extract one or mote predefined information elements; assign a priority to said token based on said extracted information elements and a state occupancy of said token, wherein said assigned priority controls an order in which said token is processed; assess an overload status of said system; and selectively discard one or more of said tokens based on said assigned priority and said assessed overload status.
 2. The state machine of claim 1, wherein said processor is further configured to dynamically adjust a priority assigned to said token based on said overload status.
 3. The state machine of claim 1, wherein said extracted information elements comprise one or more name/value pairs.
 4. The state machine of claim 1, wherein said assigned priority is based on an effect that a particular transition by said token will have on other resources.
 5. The state machine of claim 1, wherein said assigned priority is based on one or more of an amount of computation resources required by said token; a time sensitivity of said token; a determination of whether said token includes idle time and a determination of whether a response is expected by another entity to said token.
 6. The state machine of claim 1, wherein a higher priority is assigned to a token that will trigger a transition that will return one or more currently used system resources to an available status.
 7. The state machine of claim 1, wherein said processor is further configured to assign said token to one of a plurality of priority-based queues.
 8. The state machine of claim 1, wherein said processor is further configured to discard one or mole lower priority tokens when a priority queue of a predefined priority level is full.
 9. A state machine, comprising: a memory containing a flow graph associated with a system that provides a flow control mechanism, wherein said flow control mechanism defines a plurality of states and one or more transitions between said plurality of states, wherein one or more tokens circulate within said flow graph and execute functions during said one or more transitions between said states; and at least one processor, coupled to the memory, said at least one processor operative to: parse one of said tokens to extract one or more predefined information elements; assess an overload status of said system; and selectively discard one or more of said tokens based on said assessed overload status and a closeness measure indicating how close said token is to placing said system in a quiescent state.
 10. The state machine of claim 9, wherein said flow graph is a call flow graph that controls a processing of call control messages and wherein said functions include one or mote of sending messages to other tokens and to external devices; and parsing incoming messages from other tokens or external devices.
 11. The state machine of claim 9, wherein said processor is further configured to discard one or more lower priority tokens when a priority queue of a predefined priority level is full.
 12. A method for prioritizing message flows in a state machine execution environment, wherein said state machine execution environment employs a flow graph associated with a system that provides a flow control mechanism, wherein said flow control mechanism defines a plurality of states and one or more transitions between said plurality of states, wherein one or more tokens circulate within said flow graph and execute functions during said one or mote transitions between said states, said method comprising: parsing one of said tokens to extract one or more predefined information elements; assigning a priority to said token based on said extracted information elements and a state occupancy of said token, wherein said assigned priority controls an order in which said token is processed; assessing an overload status of said system; and selectively discarding one or more of said tokens based on said assigned priority and said assessed overload status.
 13. The method of claim 12, wherein said extracted information elements comprise one or more name/value pairs.
 14. The method of claim 12, wherein said assigned priority is based on an effect that a particular transition by said token will have on other resources.
 15. The method of claim 12, wherein said assigned priority is based on one or more of an amount of computation resources required by said token; a time sensitivity of said token; a determination of whether said token includes idle time and a determination of whether a response is expected by another entity to said token.
 16. The method of claim 12, wherein a higher priority is assigned to a token that will trigger a transition that will return one or more currently used system resources to an available status.
 17. The method of claim 12, wherein said flow graph is a call flow graph that controls a processing of call control messages and wherein said functions include one or more of sending messages to other tokens and to external devices; and parsing incoming messages from other tokens or external devices.
 18. The method of claim 12, further comprising the step of assigning said token to one of a plurality of priority-based queues.
 19. The method of claim 12, further comprising the step of dynamically adjusting a priority assigned to said token based on an overload status.
 20. The method of claim 12, further comprising the step of selectively discarding one or more of said tokens based on said assessed overload status and a closeness measure indicating how close said token is to placing said system in a quiescent state. 